Liquid sight indicators are used as liquid level gauges for vessel inventory estimation and sight flow monitors for piping system flow indication (bull's eye), or as observation sites for process equipment such as reactors, heaters, storage vessels and the like. Sight gauges are typically externally mounted on a vessel or pipe and connected between two mounting blocks attached within the range of liquid movement to indicate the presence and/or level of liquid therein. Gauges for visual indication employ transparent tubular conduits of an inert substance such as glass mounted between the mounting blocks. Breakage of the glass tube is a concern.
Many inventors have described sight gauges that improve safety by externally shielding the glass sight tube. These inventions are extremely useful for their stated purposes however they do not include a leak shut off system as the present invention which trips coaxially aligned check valves to a closed position when pressure changes, caused by a leak, occur in the gauge. Examples of prior art sight gauges are described in the following patents:
Wolf, U.S. Pat. No. 5,648,607 describes a replaceable sight gauge assembly which includes two bolt assemblies. Each bolt assembly includes an entry bolt and an exit bolt, the entry bolt houses a valve which is opened when the exit bolt is mated therein, the valved bolts provide a means for replacing the sight gauge.
Sheridan U.S. Pat. No. 5,628,231 describes a sight glass for steam boilers which includes and flanges provided with molded inserts which serve to provide sealing means engaging the end surface of a sight glass. A concentrically disposed guard tube is also maintained in sealed relation to the end flanges. Tie rods to prevent excess tightening of the ended flanges are also provided.
Mills, U.S. Pat. No. 5,442,159 describes a sight gauge positioned between two spaced apart compression fittings which receive an elongated tubular transparent tube shield and a slightly longer concentrically placed sight tube.
Newman, U.S. Pat. No. 5,323,654 describes a shielded sight glass positioned between two spaced apart confronting fitting which is shielded by a polygon impact resistant plastic enclosure.
Gruett U.S. Pat. No. 5,323,653 concerns a method for mechanically supporting a shield for a liquid gauge. The apparatus includes a support member, first and second end blocks which are slidable engagable with the support member while each has a passage way, sealborne by each of the end blocks and disposed in each of the passage ways and a transparent tube telescopingly received in the respective passage ways and defining a fluid passage way or chamber.
Bertani, U.S. Pat. No. 5,383,360 describes a column type level indicator with a means for its outward mounting through fixing screws with axial and transvese holes therethrough which act as ducts into the sight tube.
Ford et al. U.S. Pat. No. 5,052,224 describes a shielded vertically mounted sight gauge with a transparent pipe extending between housings, while each housing includes a flange for receiving a larger transparent shielding pipe, one flange telescopingly receives the shield with a biasing means that urges against the shield pipe so that the flange can be moved away from the shield pipe and access gained to the sight tube.
Sheridan et al. U.S. Pat. No. 4,838,095 describes a sight glass with sampling system and includes an inner transparent glass tube an outer concentric shield tube forming an interstices between the tubes and a drain for remaining leakage caused by fracture of the inner tube.
Mills U.S. Pat. No. 4,693,117 describes a shielded tubular gauge for placement between two spaced apart fittings connected to a vessel to show the level of liquid in the vessel, including an elongated sheet of protective material slidable received in the U-shaped edges of the frame.
Jackson U.S. Pat. No. 4,345,468 describes a level sight monitor which includes a double tube sight element. The internal glass element is connected to the liquid system being monitored. The external tube is transparent plastic and provides a protective shield to the internal pipe and is spaced apart from the internal tube with "O" rings fitted, preferably flanged inserts. The annulus between the two tubes can be environmentally purged.
Gruett, U.S. Pat. No. 3,886,796 describes a gauge for indicating liquid level in a tank with a transparent plastic tube disposed between a pair of hollow end members.